Cardiac arrest and stroke are two of the leading causes of mortality. An estimated 1.25 million people suffer heart attacks annually and nearly 500,000 of these die. 500,000 individuals will have strokes and roughly 30% of these will die. In both instances, many of the survivors will be severely and permanently disabled as a result of injury to their central nervous systems. To date there have been no clinically effective pharmacologic tools for amelioration of brain damage arising from a stroke or cardiac arrest. Ischemia results in a massive release of the excitotoxic amino acids, glutamate and aspartate, into the extracellular environmental of the brain, precipitating an influx of calcium into cells. Intracellular calcium in turn activates various calcium-dependent enzymes, including nucleases, proteases and phospholipases, resulting in a chain of events, including lipolysis, during ischemia, and free fatty acid metabolism and generation of superoxide radicals during reperfusion. Free radicals can initiate a chain reaction of lipid peroxidation, with extensive destruction of plasma and mitochondrial membranes and failure of cellular homeostasis and metabolism. To reduce the neurologic morbidity associated with resuscitation int cardiac arrest or stroke, it will be necessary to understand the molecular mechanisms underlying reperfusion injury with delayed neuronal death. A rat four vessel occlusion (o) model of cerebral ischemia/reperfusion will be used to assess the degree of o injury as revealed by the rate of glutamate, aspartate, gamma-aminobutyric acid, adenosine and inosine efflux into the interstitial spaces of the rat cerebral cortex. The role of phospholipases in the release of these substances will be assessed with the use of specific inhibitors of these enzymes, and of the protein kinases which activate phospholipase. Further evidence of phospholipase activation will be sought by applying these enzymes directly onto the cerebral cortex and measuring amino acid and purine release. An involvement of free radicals in amino acid and purine efflux during ischemia/reperfusion will be assessed by preventing free radical action with inhibitors of the enzymes responsible for their formation or by the artificial generation of free radicals in the cerebral cortex. A chronic rat 4VO model will be used to evaluate the ability of phospholipase inhibitors to prevent ischemia/reperfusion injuries, manifested as neurological disabilities and hippocampal CA1 pyramidal cell injury. Overall, these experiments should provide definitive evidence on the molecular mechanisms responsible for neuronal injury and death,a with significant implications for the development of novel therapeutic approaches to the prevention and treatment of ischemia/reperfusion induced brain damage.